Compounds such as organic matter and nitrogen contained in wastewater are capable of being oxidized and transformed by bacteria which use these compounds as a food source. Typically, heterotrophic bacteria digest the organic matter while nitrifying bacteria use the non-carbon compounds, for example, oxidizing ammonia to nitrate (a process know as nitrification to those skilled in the art).
The prior art, for example the US Environmental Protection Agency Manual on Nitrogen Control (USEPA, 1993); Wastewater Engineering, Treatment and Reuse, 4th Edition (Metcalf and Eddy, 2003); Small and Decentralized Wastewater Management Systems (Crites and Tchobanoglous, 1998); and Design and Retrofit of Wastewater Treatment Plants for Biological Nutrient Removal (Randall et al., 1992), teaches that nitrifying bacteria are much more cold sensitive and as a consequence the nitrification process virtually ceases when the water temperature approaches 4° C.
A common form of biological wastewater treatment is the sewage treatment lagoon and these lagoons typically discharge elevated levels of ammonia during winter months in regions in which the water temperatures approaches 4° C. or lower. In view of changing environmental regulations, it would be highly advantageous to develop a biological treatment process that could remove ammonia at water temperatures of less than 4° C.
U.S. Pat. No. 6,200,469 and related U.S. Pat. Nos. 6,406,627 and 6,652,743 teach a system for removing pollution from water, utilizing a subsurface constructed wetland system using forced bed aeration and variable water levels to establish staged anaerobic and aerobic zones within the system. This prior art is relevant to the current invention because it teaches a method for delivering oxygen to the wastewater via aeration in a system utilizing attached-growth bacteria for treatment. However, the prior art does not teach a method for improved removal of ammonia at water temperatures approaching 4° C.